Some computer software publishers update their software applications (computer programs and data files associated with the programs) frequently. These updates often add new features to the applications as well as remove existing bugs. Several methods are commonly used to update software applications. The simplest of these is to distribute one entire software application to replace an older one. This full update method is simple, but expensive and inconvenient. Typically the software is distributed on some type of removable media, such as floppy disks or CD-ROM's, which are costly to produce and distribute. The time an end user must wait for the removable medium to arrive and the time it takes for the software application to install itself on a computer system are inconvenient. This inconvenience is compounded where updates occur frequently.
Because of the large size of many software applications it is generally not feasible to distribute full updates over computer networks, such as the Internet. When full updates of larger applications are distributed over a network, they often cause such high loads on servers that other users suffer slow-downs on the network, and the servers have trouble meeting the demands.
In order to bypass many of the problems associated with this type of software updating, some software publishers distribute incremental updates. These incremental updates do not contain entire software applications, but rather they contain that information which is necessary to transform a particular version of a software application to a newer version. As used herein, the word "version" indicates a file or application of a specified state. Among the methods available to perform such incremental software updating is binary patching, performed by programs such as RTPatch, published by Pocket Soft, Inc. A binary patcher changes those binary bits of a computer readable file which are different in a newer version. A binary patcher needs, in addition to the old file, a data file which includes the differences between the two versions. Because most software updates involve changes to only a small portion of a software application, incremental update files are generally small. The smaller data files distributed for a binary patch incremental update are often less than 1% of the size of a full update, taking advantage of the large amount of redundancy in the two versions.
The use of incremental update methods allows for smaller updates which can be distributed by means which are not conducive to the distribution of full updates, such as distribution over the Internet. The smaller incremental updates also make distribution by floppy disk more feasible where a full update would have required many disks, and an incremental update may require only one.
However, incremental update methods introduce another problem: an incremental update is specifically useful for updating only one particular version of a software application to another particular version. When updates occur frequently, as with virus protection software applications, end users may update from an arbitrarily old version to the newest version, skipping over several previously released versions. An incremental update for the newest version of a software application will generally update only from the most recent version, however. To update from an arbitrarily old version to the most recent version with incremental updates, a user often needs to acquire and apply a number of successive incremental updates.
One solution to this problem has been for software publishers to group a number of incremental update files together into one distribution. Each necessary incremental update is applied, one at a time, to update to the newest version. However, the number of incremental updates may be large, due to the fact that a grouping generally covers a large number of possible versions. The benefits of smaller distributed update files begin to disappear, as the size of the grouped-together incremental updates grows. Lowering the number of update files available increases the amount of data the average user must acquire for an update, since the user will not need all of the incremental updates in a grouping. This method of updating applications can also be cumbersome, as a series of incremental updates needs to be selected from the group and applied to the software application one after another.
Another solution to the problem of incremental update version-specificity has been to create many unique incremental update files which each transform a different previous version to the most current version. Then, only one incremental update is needed by any user. However, where updates are very frequent, this scheme results in a large number of incremental update files to produce, store and maintain for users. In the case of publishers, such as virus-protection software publishers, who might update their applications as often as daily, this can quickly become untenable. The number of files which must be made available with this scheme grows quickly, and makes the mirroring of incremental updates on a local server almost impossible. For example, in a case where a virus protection software publisher makes new virus definition files available daily, each year's worth of updates will require approximately 365 incremental update files.
One alternative to the methods described above is the use of "push" technology, in which a server maintains a database of what version each user has. The server then sends the necessary updates to each user, as they become available. This system requires "smart" servers, however, to monitor user configurations, to determine what each user needs, and to send the appropriate update information. This results in a server-intensive system which can cause a drain on server resources comparable to that experienced in the full update scheme, when many users are simultaneously requesting full updates. It is preferable to use a system which allows update files to be stored on a "dumb" server which simply provides specifically requested files.
What is needed is a system for updating software applications from an arbitrary first version to a newer version without requiring a large amount of information to be stored and maintained by an update server, without requiring a user to acquire a large amount of data to perform each update, and without requiring the use of "smart" servers.